1911.] rUBLIC DOCUMENT — No. 31. 305 



coiiii)ilati()n every five years, however, insures quite reliable 

 figures in most instances. In case of the agricultural chemicals 

 and by-products which are commonly known to the fertilizer 

 trade, the present compilation includes the samples collected by 

 our inspectors during the last five years, as well as those samples 

 sent by farmers and farmer organizations. In all cases where 

 samples are forwarded for analysis, they are taken according to 

 printed directions furnished from this office, which is a reason- 

 able assurance that the analyses are representative of the mate- 

 rials samjiled. In many instances extremely wide variations 

 occur in dift'erent analyses of the same product. This empha- 

 sizes the importance of careful sampling as well as the purchase 

 of such materials on a specific guarantee of plant food which 

 they furnish. 



In the majority of instances only the highest, lowest and 

 average percentage of nitrogen, potash and phosphoric acid are 

 given in the tables, but it should be remembered that blanks do 

 not imply the absence of the other ingredients. 



